Why?

My 4th grade granddaughter asked me last night, "Why did Chris kill himself? He had a little girl. I feel so sorry for her."
I know Chris. I know his parents. I know his brother. I know his ex-wife.
Many people are hurt over his loss. In fact his father went into heart failure when called to come identify his son. He is okay physically now, but emotionally ....
This man, the father, has helped his son emotionally as well as financially. His son married a younger girl on her word of how terrible her parents were. She moved in with them. Got pregnant and then when she graduated, divorced him. Made his life a living hell for many years. His father and mother fought for his rights to visit his daughter without supervised visits. He finally got them.
I can not answer my granddaughter's question of why. I have heard many rumors... mainly of a girlfriend break-up. One of this young man's best friends commit suicide just a few months ago... same way... over a break-up with his girlfriend.
So how do you explain such a tragedy? How do you comfort the family? I have "written" a letter to his family in my head numerous times in the past 24 hours... just nothing seems to fit.